Understanding Lithium-Mediated Oxygen Reactions at the Au|DMSO interface: Are We There?

Abstract

Lithium–oxygen (Li–O2) batteries have received much attention in recent years due to their ultrahigh theoretical specific energy that could transform current energy storage, should a practical device be realized. At the fundamental level, substantial progress in the understanding of the reactions and processes occurring in Li–O2 batteries has been made; however, significant disputes still remain for the operational mechanisms. Herein, we demarcate the scope of this review to the lithium-mediated oxygen reactions at the Au|DMSO interface. As regards this model electrochemical interface, we first summarize the current understandings of the oxygen reaction mechanisms and the dynamic reaction interfaces, and then, we offer our perspectives on the remaining issues and puzzles, including how the oxygen reaction mechanisms and their associated interfaces are influenced by the electrode surface conditions, the electrolyte compositions, the sensitivity and spatiotemporal resolution of characterization methods, and the operating conditions of the Li–O2 batteries.

Unraveling the Unstable Nature of Tetraglyme-Based Electrolytes toward Superoxide and the Inhibitory Effect of Lithium Ions by Using In Situ Vibrational Spectroscopies

“…On the other hand, the in situ IRRAS can evaluate the reaction species in the thin layer between the electrode and the optical window and on the electrode surface. A commercially available FTIR in the IRRAS can obtain an infrared spectrum covering a wide frequency region. − In addition, in situ SERS can sensitively detect the surface-adsorbed species on the SERS-active substrate during the reaction process. − SERS measures a change in polarizability during the vibration and has a different spectroscopic selectivity rule with IRRAS, which probes the vibrational transition of dipole moment. SFG spectroscopy requires that the vibrational transition is both infrared and Raman active.…”

The Decisive Role of Li2O2 Desorption for Oxygen Reduction Reaction in Li–O2 Batteries

“…Recently, Tan et al reported a TOF-SIMS study for ORR on a gold electrode in a DME-based electrolyte solution and concluded that major ORR sites located at the interface between gold and Li 2 O 2 . However, the reaction conditions (such as electrode materials, electrolyte compositions, and cell structures) and characterization techniques are different in these studies, which makes it hard to achieve consistency for the reaction interface of ORR (Scheme a,b) by just comparing current results. , …”

“…Many relevant issues are controversial with the lack of a self-consistent theory. 11,12 The primary problem lies in its discharge process (i.e., oxygen reduction reaction (ORR)), which directly affects the surface state of ORR products, such as lithium peroxide (Li 2 O 2 ) and lithium superoxide (LiO 2 ). 13,14 During the initial discharge stage for Li−O 2 batteries, it is generally recognized that electrochemical reaction steps of ORR in the aprotic electrolyte solution (reactions 1 and 2) occur on the electrode surface, where * denotes the adsorbed species as O 2 *, LiO 2 *, and Li 2 O 2 *.…”

“…31 However, the reaction conditions (such as electrode materials, electrolyte compositions, and cell structures) and characterization techniques are different in these studies, which makes it hard to achieve consistency for the reaction interface of ORR (Scheme 1a,b) by just comparing current results. 11,12 If the controversy about the reaction interface of ORR is expected to be resolved fundamentally, it is necessary to figure out the reasonability of the corresponding mechanism in detail. When the ORR occurs at the Li 2 O 2 /electrolyte interface (Scheme 1a), the electrons must pass through the Li 2 O 2 layer for the electro-reduction of oxygen molecules.…”

“…This bottleneck to further optimization of Li–O 2 batteries is related to elucidating its reaction interface and mechanism. Many relevant issues are controversial with the lack of a self-consistent theory. , The primary problem lies in its discharge process (i.e., oxygen reduction reaction (ORR)), which directly affects the surface state of ORR products, such as lithium peroxide (Li 2 O 2 ) and lithium superoxide (LiO 2 ). , …”